Monoclonal Antibodies in the Therapy
In an ongoing quest to improve the therapeutic arsenal against cancer, a fourth weapon other than surgery, chemotherapy and radiotherapy has emerged, i.e. targeted therapy. Targeted therapy includes tyrosine kinase receptor inhibitors (small molecule inhibitors like imatinib, gefitinib, and erlotinib), proteasome inhibitors (bortezomib), biological response modifiers (denileukin diftitox) and monoclonal antibodies (MAbs). The remarkable specificity of MAbs as targeted therapy makes them promising agents for human therapy. Not only can MAbs be used therapeutically to protect against disease, they can also be used to diagnose a variety of illnesses, measure serum protein and drug levels, type tissue and blood and identify infectious agents and specific cells involved in immune response. About a quarter of all biotech drugs in development are MAbs, and about 30 products are in use or being investigated. A majority of the MAbs are used for the treatment of cancer. (Gupta, N.; et al., Indian Journal of Pharmacology 38 (2006) 390-396; Funaro, A.; et al., Biotechnology Advances 18 (2000) 385-401; Suemitsu, N. et al., Immunology Frontier 9 (1999) 231-236)
Labeled Monoclonal Antibodies and In-Vivo Imaging
Several in vivo imaging methods are available for the quantification of therapeutic antibodies in tumor tissue usually based on labeled derivatives of the antibodies. Said labeled antibodies usually include antibodies labeled with radiolabels such as, e.g. 124I, 111In, 64Cu, and others, for use in positron emission tomography (PET) (see e.g. Robinson, M. K., et al., Cancer Res 65 (2005) 1471-1478; Lawrentschuk, N., et al., BJU International 97 (2006) 916-922; Olafsen, T., et al., Cancer Research 65 (2005) 5907-5916; and Trotter, D. E., et al., Journal of Nuclear Medicine 45 (2004) 1237-1244), 123I, 125I, and 99mTc and others for use in single photon emission computed tomography (SPECT) (see e.g. Orlova, A., et al., Journal of Nuclear Medicine 47 (2006) 512-519; Dietlein, M., et al., European Journal of Haematology 74 (2005) 348-352).
Also nonradioactive labels are known for in-vivo imaging techniques, e.g. near-infrared (NIR) fluorescence labels, activatable dyes, and engodogenous reporter groups (fluorescent proteins like GFP-like proteins, and bioluminescent imaging) (Licha, K., et al., Adv Drug Deliv Rev, 57 (2005) 1087-1108). Especially NIR fluorescence imaging can be used for the quantification of therapeutic antibodies in tumor tissue. Advantages of near infrared imaging over other currently used clinical imaging techniques include the following: potential for simultaneous use of multiple, distinguishable probes (important in molecular imaging); high temporal resolution (important in functional imaging); high spatial resolution (important in vivo microscopy); and safety (no ionizing radiation).
There exist different monoclonal antibodies covalently coupled to a NIR fluorescence label (Hilger, I., et al, Eur Radial (2004) 1124-1129; Ballou, B., et al., Cancer Immunol Immunother. 41 (4) (1995) 257-63; Ballou, B., et al., Proceedings of SPIE—The International Society for Optical Engineering 2680 (1996) 124-131; Ballou, B., et al., Biotechnol Prog. (1997) 649-58; Ballou, B., et al., Cancer detection and prevention (1998), 22 251-257 Becker, A., et al., Nature Biotechnology 19 (2001) 127-131; Montet, X., et al., Cancer Research 65 (2005), 6330-6336; Rosenthal, E. L., et al., The Laryngoscope 116 (2006) 1636-1641; EP 1619501, WO 2006/072580, WO 2004/065491 and WO 2001/023005) which were used as single agents for NIR fluorescence imaging.
In NIR fluorescence imaging, filtered light or a laser with a defined bandwidth is used as a source of excitation light. The excitation light travels through body tissues. When it encounters a near infrared fluorescent molecule (“contrast agent”), the excitation light is absorbed.
The fluorescent molecule then emits light (fluorescence) spectrally distinguishable (slightly longer wavelength) from the excitation light. Despite good penetration of biological tissues by near infrared light, conventional near infrared fluorescence probes are subject to many of the same limitations encountered with other contrast agents, including low target/background ratios.
Near infrared wavelengths (approximately 640-1300 nm) have been used in optical imaging of internal tissues, because near infrared radiation exhibits tissue penetration of up to 6-8 centimeters. See, e.g., Wyatt, J. S., and Kirkpatrick, P. J., Phil. Trans. R. Soc. B 352 (1997) 701-705; Tromberg, et al., Phil. Trans. R. Soc. London B 352 (1997) 661-667.
The exact amounts of the antibody-label conjugates used for in vivo imaging depends on the different characteristics and aspects of the labels used, e.g. for NIR fluorescence labels the quantum yield of the label is one of the criteria for the amount of label or labeled antibody used (see e.g. WO 2006/072580).
Therapy Monitoring During Treatment with Monoclonal Antibodies
Factors affecting the successful therapy of malignant diseases include the antibody dose used and the schedule of administration, the half-life and fast blood clearance of the antibodies, the presence of circulating antigen, poor tumor penetration of the high/mol.-wt. monoclonal antibody (MAb) and the way in which these molecules are catabolized. At present, there is a lack of knowledge about many aspects of the physiological function and metabolism of antibodies. (Iznaga-Escobar, N. et al, Meth. Find. Exp. Clin. Pharm. 26(2) (2004) 123-127). Therefore it is important to monitor the course of such therapies.
The success of such treatments is usually assessed using different imaging techniques like chest X-ray, computed tomography (CT), computerized axial tomography (CAT), molecular resonance imaging (MRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), fluorescence imaging (FI), and bioluminescent imaging (BLI) (see e.g. Helms, M. W, et al., Contributions to microbiology 13 (2006) 209-231 and Pantel, K., et al., JNCI 91 (1999) 1113-1124). It is often defined as a “Response” to the treatment. According to RECIST criteria tumor response for solid tumors (Therasse, et al., J. Nat. Cancer Institute. 92 (2000) 205-216) is categorized in dependency of the volume progression or regression of the tumors (e.g. measured via CT) into four levels: complete response (CR) or partial response (PR), stable disease (SD) and progressive disease (PD) (see Table 1). Furthermore the European Organization for Research and Treatment of Cancer (EORTC) proposed a categorization into four levels in dependency of the metabolism of the tumors measured via 2-[18F]-Fluoro-2-deoxyglucose positron emission tomography (FDG-PET) (Young, H., et al., Eur J Cane 35 (1999) 1773-1782 and Kelloff, G. J., et al, Clin Cane Res 11 (2005) 2785-2808): complete metabolic response (CMR) or partial metabolic response (PMR), stable metabolic disease (SMD) and progressive metabolic disease (PMD) (see Table 2). Recently a combined assessment with CT and PET gets more and more common. While CT mainly focuses on the development of tumor size it delivers only restricted information on the tumor metabolism and is associated with exposure to radioactive radiation, PET imaging gives more insight in the tumor metabolism, but still radioactive labels are needed for this technique.